The present invention relates to a coreless induction furnace for processing metal or metal melts, such as melting of metals or holding heat in metals, particularly in vacuum or under overpressure.
Induction furnaces of the foregoing type include a cooled induction coil, the windings of which together with intermediate layers of flexible gas-tight material, such as rubber, inserted between the windings, form a portion of the outer gas-sealed jacket of the furnace crucible. The windings of the coil and its intermediate layers are compressed in the axial direction of the coil by a clamping device.
The induction coil of the type under consideration is disclosed in DE-PS No. 496,462. This coil includes intermediate layers of, for example rubber, inserted between the windings of the coil and surrounding the interior of the furnace crucible. The whole arrangement comprised of the coil windings and intermediate layers is compressed by means of a special arrangement which is engaged with lower and upper plates provided on the end sides of the induction coil. Since the pressure, with which the windings and the intermediate layers are pressed together, is to be high in order to obtain a gas-sealed jacket of the crucible of the furnace considerable forces act on the intermediate layers formed of resilient material. In practice, it is not only impossible to overcome these forces so that only axial forces would exert in the coil, but various loads on the intermediate layers at various places of the coil in the axial and circumferential directions would unavoidably result in the induction coil. Such a non-uniform force distribution leads to the fact that radially-acting forces occur, which cause a lateral movement of the portions of the induction coil and the intermediate layers.
In order to overcome the above-described problem it has been proposed, for example in DE-PS No. 2,420,533 to provide externally of the coil a number of iron yokes uniformly distributed around the coil in the circumferential direction. These yokes firstly serve for a field-force guiding, and secondly for pressing the coil toward the crucible of the furnace. With this means, however, it has not been attained that forces acting on the intermediate layers of resilient material would be uniformly distributed on the intermediate layers of the coil. It has been observed that these forces have been more or less non-uniformly distributed whereby at certain places of the coil where only small compressing forces occurred, a gas-tight sealing has not been possible. A considerable axial pressure prevails at some individual spots of the intermediate layers so that the material of these layers has been strongly loaded while at other spots of the intermediate layers a very small pressure has exerted, which has been not sufficient for the gas-tight sealing of the furnace.